by Jolie Lee and Jessica Durando, USA TODAY

by Jolie Lee and Jessica Durando, USA TODAY

All 298 people aboard Malaysia Airlines Flight MH17 were killed when the airliner crashed Thursday in eastern Ukraine at Russia's border.

As the investigation unfolds, USA TODAY Network rounds up what we know and the questions left unanswered.

What happened?

The United States says a surface-to-air missile took down the jet. The Boeing 777 was flying over Ukraine's war-torn Donetsk region, the site of fighting between Ukraine and pro-Russian Ukrainian separatists.

Vice President Biden said the crash was "not an accident. It was blown out of the sky." Ukrainian Prime Minister Arseniy Yatsenyuk called the attack an "international crime." President Obama called it a "global tragedy."

Who took down the jetliner?

The Pentagon said Friday it is unlikely that pro-Russian separatists in east Ukraine could obtain or operate the sophisticated missile system allegedly used to shoot down the Malaysia Airlines plane without Russian help.

The Pentagon says there is strong evidence the missile, a SA-11, was fired by Russian-backed separatists since the missile was fired from an area controlled by rebels.

The Obama administration said preliminary evidence suggests the aircraft was hit by a surface-to-air missile. Ukraine's government says the jetliner was shot down by a Russian aircraft.

Who was on board the flight?

The jetliner was carrying 298 people, including 80 children. The victims came from 11 countries. They included an acclaimed AIDS researcher from Amsterdam, a nun and teacher from Sydney, a Dutch senator, a Malaysian actress and a World Health Organization spokesman.

World leaders demanded Friday that pro-Russia rebels who control the crash site give immediate, unfettered access to independent investigators to determine who took down the plane.

About 30 officials, mostly from the Organization of Security and Cooperation in Europe, arrived at the crash site. The rebels allowed the officials to carry out a partial and superficial inspection.

Australian Prime Minister Tony Abbott on Saturday warned that any party that tries to block access to or contaminate the crash site is "no friend of justice" and "no friend of peace."

"Australia takes a very dim view of countries which facilitate the killing of Australians. The idea that Russia can wash its hands of responsibility because this happened in Ukrainian airspace just does not stand up to serious scrutiny. We all know what's happening in the Ukraine," he said.